Due to advantages of high rate and low costs of a wireless local area network (WLAN for short), the wireless local area network becomes one of mainstream mobile broadband access technologies nowadays. A Media Access Control (MAC for short) layer of an existing WLAN performs data transmission by using a contention mechanism of carrier sense multiple access with collision avoidance (CSMA/CA for short). A sending node monitors energy of a channel before sending data. If the energy of the channel exceeds a CCA threshold, it is considered that the channel is busy. If the energy of the channel is less than the CCA threshold, it is considered that the channel is clear. When the channel is clear, the sending node performs channel contention. To increase a data thoughput rate of a WLAN system, the CCA threshold may be increased, to increase a possibility of link transmission. However, in an actual communications system, increasing the CCA threshold may, instead, reduce a system throughput.